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Development of LLTV techniques for detection/analysis of spectra with application top cephei stars and other objects

University of British Columbia

New techniques for the detection and analysis of astronomical spectra have been developed and applied successfully in a study of the spectral variations of β Cephei stars and other objects of astrophysical interest. The method involves the replacement of the photographic plate as the detection and recording medium by a television camera and an associated data acquisition system, with resulting improvements in sensitivity, precision, and facility of data reduction. The system limitations have been set primarily by the particular television camera selected, with important deficiencies being degraded resolution and a limited integration capability. This paper follows, from one viewpoint, development of the system hardware, assessment of the system potential and its subsequent application to astrophysical problems, development of the software package for optimal data retrieval, and interpretation of the results within the framework of current theory. The results and contributions are discussed under two headings: (i) Engineering Development and (ii) System Applications. (i) Engineering Development The operation of many detectors used in astronomy benefits from an environment of reduced and stabilized temperature. Such is the case for the television detectors used in this program. As a consequence, a cooling system was developed for an Image Isocon tube, the prime detector employed. This system circulates cold air through the yoke of the television camera in a closed circuit and cools the tube uniformly by forced convection. It satisfies the requirements for successful operation of the Isocon and has general value in demonstrating (a) the feasibility of an air-cooling approach in situations of awkward geometry or unusual heat dissipation and (b) that the hardware associated directly with a detector can be simple, compact, and inexpensive. (ii) System Applications The capability of the detection system for improved time resolution spectroscopy was of particular benefit in examining the short-term spectral changes in the β Cephei stars, a group distinguished by their regular variation in light and radial velocity. The stars a Virginis (Spica), β Cephei, and BW Vulpeculae, representing some of the extremes in variability within the group, were observed in 1971 and 1972. The observations of Spica, the first of the program, served to demonstrate the value of the new instrumentation for this application. Marked gains were made in the case of BW Vul where, for the first time, sufficient time and spectral resolution were attained to resolve the very rapid spectral variations occurring at certain phases of its pulsation cycle. The observations made possible a more accurate determination of the dynamic properties of its atmosphere and critical tests of 'models' attempting to explain its variation. A refined picture is presented of this variation, taking as its basis the shock wave 'model' of Odgers (1956). The long-term variation in BW Vul's period and in the amplitudes of its light and velocity curves were also considered. The present data, viewed in context with that obtained over the past fifty years, demonstrate the existence of a pseudo-sinusoidal variation in the pulsation period, super- imposed on a mean rate of increase of +3.7 sec/century, plus a secularly increasing velocity amplitude. Thus the pulsation amplitude is also increasing and the star may be in a rapid phase of evolution. For β Cep, the first definitive record of a variation in line profile correlated with its variation in light and radial velocity was obtained. The result is critical to an understanding of its pulsation. In summary, the main astronomical program has provided information important in understanding the physical processes occurring in the β Cephei stars and has demonstrated the value of a new type of instrumentation for studies of rapid spectrum variables.

Text

2011-03-03

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http://hdl.handle.net/2429/31957

Astronomy

University of British Columbia

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